Color display screen employing two layers of phosphors,particles in the inner layer being small with respect to those in the outer layer and discontinuous in coverage



June 23, 3970 M. E. JONES A 3,517,243

coLoR DISPLAY SCREEN EMPLOYING TWO LAYERS OF PHOSPHORS, PARTICLES IN THEINNER LAYER BEING SMALL'WITH RESPECT TO THOSE IN THE OUTER LAYER ANDDISCONTINUOUS IN COVERAGE Original Filed Dec. 2, 1966 2 Sheets-Sheet 1RED GREEN A BLUE ELECTRONIC SWITCH 53\ H'GH L VOLTAGE 51 SWITCH FiG.2.

June 23, 1970 -1E-,- JONES 3,517,243

COLOR DISPLAY SCREEN EMPLOYING TWO LAYERS OF PHOSPHORS, PARTICLES IN THEINNER LAYER BEING SMALL WITH RESPECT TO THOSE IN THE OUTER LAYER ANDDISCONTINUOUS IN COVERAGE Original Filed Dec. 2, 1966 2 sheets sheet 2760 (I) L-J E I @40- 5: ID

ACCELERATING VOLTAGE United States Patent 3,517,243 COLOR DISPLAY SCREENEMPLOYING TWO LAY- ERS 0F PHOSPHORS, PARTICLES IN THE INNER LAYER BEINGSMALL WITH RESPECT TO THOSE IN THE OUTER LAYER AND DISCON- TINUOUS INCOVERAGE Morton E. Jones, Richardson, Tex., assignor to TexasInstruments Incorporated, Dallas, Tex., a corporation of DelawareContinuation of application Ser. No. 598,828, Dec. 2, 1966. Thisapplication Mar. 17, 1969, Ser. No. 808,010 Int. Cl. H01j 29/26 US. Cl.313-92 6 Claims ABSTRACT OF THE DISCLOSURE Disclosed is a color displayscreen that produces light of different colors in response to impingingelectrons of different energies, characterized by having a first layerof phosphors which emits light of a first color when energized byelectrons having energies above a relatively high predetermined level,and a discontinuous layer of small particles of a second phosphoroverlying the first layer and emitting light of a second color whenenergized by electrons having energies above a relatively lowpredetermined level, the particles of the second phosphor beingrelatively small in relation to the thickness of the first layer andbeing of a size such that electrons having energies above the relativelyhigh energy level pass through the particles without giving upsubstantial energy and produce substantially no more light of the secondcolor than is produced by electrons having energies just equal to orbelow the relatively high level. In this way the electrons having energyabove the relatively high level excite the phosphors in the first layerto produce an increasing amount of said first color with increasingelectron energies but without producing substantial increases in theamount of the second color which is emitted by the particles of thesecond phosphor.

This application is a continuation of copending application, Ser. No.598,828, filed Dec. 2, 1966.

This invention relates to a color display screen and more particularlyto such a screen which produces light of different colors in response toimpinging electrons of different energies.

Among the several objects of the present invention may be noted theprovision of a novel color display screen which produces light in a widerange of different colors in response to impinging electrons ofdifferent energies; the provision of a color display systemincorporating such a screen which comprises a plurality of differentcolor phosphors, which phosphors are cumulatively energized by electronsof increasing energy; the provision of such a system in which the lightoutput from the first phosphor energized does not increase substantiallywith increasing electron energies above a predetermined level wherebythe contribution of color from said first phosphor may be controlled;the provision of such a screen which is relatively simple to constructand is relatively inexpensive. Other objects and features will be inpart apparent and in part pointed out hereinafter.

Briefly, a color display screen according to this invention is operativeto produce light of different colors in 3,517,243 Patented June 23 1970ice response to impinging electrons of different energies. The screenincludes a first layer of a first phosphor which when energized byelectrons having energies above a relatively high predetermined levelemits light of a first color. This first layer is overlaid with adiscontinuous layer of particles of a second phosphor which whenenergized by electrons having energies above a relatively lowpreselected level emits light of a second color. The particles of thissecond phosphor are relatively small in relation to the thickness of thefirst layer and are scattered over the first layer with gaps between theparticles. The particles are of such size that electrons having energiesabove the relatively high energy level can pass through the particlesproducing substantially no more light of the second color than isproduced by electrons having energies just equal to that relatively highlevel. Those electrons which have energies above the relatively highenergy level and which pass through the gaps strike the first layer andproduce light of the first color in amounts which increase withincreasing electron energies. Thus, electrons having energies below therelatively high energy level produce light of the second color, andelectrons having energies above the relatively high energy level producelight of a color which is a mixture of a limited amount of the firstcolor with an amount of the second color which increases with increasingelectron energies.

The invention accordingly comprises the constructions hereinafterdescribed, the scope of the invention being indicated in the followingclaims.

In the accompanying drawings, in which one of various possibleembodiments of the invention is illustrated,

FIG. 1 is a schematic diagram of a color display system employing akinescope having a screen according to this invention;

FIG. 2 is a view illustrating, in section, various phosphor particlesemployed in the screen of FIG. 1; and

FIG. 3 is a graph representing the response of the different phosphorparticles to impinging electrons of different energies.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

Referring nOW to FIG. 1, there is indicated at 11 an electron displaytube such as the kinescope of a color television receiver. Tube 11 has aviewing screen 13 including a transparent glass face plate 15 on theinterior surface of which is deposited a light-emitting phosphor screen17. Phosphor screen 17 includes a first layer 19 which comprises arandom mixture of a multiplicity of two kinds of discrete phosphorparticles 21 and 23 both of which emit light of relatively shortwavelengths when energized. Phosphor particles 21 emit green light whenstruck by electrons having energies above a first relatively high levelor threshold and phosphor particles 23 emit blue light when struck byelectrons having energies above a second, also relatively high,threshold or level. The threshold for the blue particles 23 ispreferably higher than that of the green particles 21. Particles 21 and23 may be made differently responsive to electrons of different energiesor velocities by providing these particles with surface barrier layersof appropriate thicknesses. In FIGfZ the particles 21 are illustrated ascomprising a core particle 25 of a conventional green phosphor such assilver-activated zinc-cadmium sulfide, the ratio of zinc to cadmiumbeing about :20, coated with a relatively thin surface barrier layer 27.Particles 23 are illustrated as comprising a core particle 29 of aconventional blue phosphor such as silver-activated zinc sulfide coatedwith a relatively thicker surface barrier layer 31. The Overall sizes ofparticles 21 and 23 are, for example, on the order of about 16 microns.

Barrier layers 27 and 31, may, for example, be provided by depositingsilicon dioxide on the surfaces of the particles as disclosed incopending application Ser. No. 459,582, filed May 28, 1965, now U.S.Pat. No. 3,408,223, issued Oct. 29, 1968, or by forming in situ barrierlayers by reacting the material of the phosphor particles with amaterial which forms a nonfluorescing barrier layer on the surface of aparticle as disclosed in copending application Ser. No. 561,815, filedJune 30, 1966, now U.S. Pat. No. 3,449,148, issued June 10, 1969. Thebarrier layers formed by either of these methods cause electronsimpinging upon the particles 21 or 23 to lose energy in traversing thebarrier layer so that, unless the electron energy exceeds apredetermined level or threshold which depends upon the thickness andnature of the barrier layer, the fluorescent core particle 25 or 29 isnot excited. In general, the threshold or level which must be exceededbefore the core phosphor particle is excited to emit light may becontrolled by varying the thickness of the barrier layer. Particles 21and 23 may be applied to the interior surface of face plate 15 byflushing on the glass a thin liquid slurry of a homogeneous or randommixture of particles 21 and 23 suspended in a suitable vehicle, followedby pouring off of any excess and evaporation to form a thin dry layer 19of phosphor particles.

On top of this phosphor layer 19 there is deposited a discontinuouslayer 32 or scattering of very small particles or aggregates ofparticles 33, e.g., in the Order of about 0.1 to 1 micron in diameter,of a red light-emitting phosphor. These particles are thus quite smallin relation to the thickness of layer 17 or to the size of the particles21 and 23. Particles 33 emit light of wavelengths which are relativelylong as compared with the green and blue light emitted by the particles21 and 23 respectively. An example of a phosphor which may be ballmilled to such small sizes Without losing its fluorescent properties iseuropium-activated yttrium vanadate (YVO -Eu). Other rare-earthphosphors such as either yttrium oxide or gadolinium oxide bothactivated with europium, may also be reduced to such fine sizes Whileretaining their light-emitting qualities. The particular size of theparticles 33 is chosen in relation to the thicknesses of the barrierlayers 27 and 31, particularly the thinner layer 27, so that electronshaving energies high enough to activate either of the particles 25 and29 will also have suflicient energy to pass through the particles 33.This is not to say that such electrons having passed through a particle33 will then have suflicient energy to penetrate either of the barrierlayers 27 or 31 and to excite the underlying phosphor core particle.Rather, the particles 33 are scattered with substantial gaps 34therebetween so that large portions of the layer 19 are not masked bythe particles 33. The particles 33 may, for example, be settled over thelayer 19 from a water or air suspension, or may be deposited byelectrophoresis. They may also be applied in a film-forming vehicle asare the particles 21 and 23.

Tube 11 also includes an electron gun 41 for generating a beam 43 ofelectrons which is moved in a rasterscanning pattern across phosphorscreen 17 by any conventional means and circuitry (not shown). Gun 41includes an electron emissive cathode 45 and a grid 47 for modulatingthe beam current or number of electrons in beam 43. By means of anelectronic gate or switch 49. the beam current is modulated successivelyduring sequential time intervals by electronic signals which representred, green, and blue color records respectively, e.g., the red, green,blue information signals derived in conventional color televisionreceivers. The switching from one color signal to another may be done ona se- 4 quential frame, dot or line basis, and synchronized by means ofa signal applied at a terminal 51.

A high voltage switch 53 is provided to synchronously switch a highvoltage applied to screen 17 so that: While the current is beingmodulated in accordance with the red signal a first, relatively lowaccelerating voltage is applied between the phosphor screen 17 andcathode 45, e.g., l2 kilovolts; while the beam current is beingmodulated in accordance with the green signal the accelerating voltageis increased to a second, relatively high level, e.g., 18 kilovolts; andwhile the beam current is being modulated in accordance with the bluesignal the accelerating voltage is increased to a third, even higherlevel, e.g., 24 kilovolts. Since the electrons which constitute beam 43have different electron velocities or energies at difierent times,deflection compensation is provided by any suitable conventional meansso that the electrons of different velocities are maintained in registrythroughout the raster-scanning pattern.

The light output or response of the particles 33, 21, and 23 toexcitation by electrons having different energies or velocities isillustrated by the curves 33A, 21A, and 23A in FIG. 3, light output inarbitrary units of brightness being indicated on the ordinate andaccelerating voltages expressed in kilovolts being represented on theabscissa. As will be seen from FIG. 3, the particles 33 emit red lightwhen the electron energies exceed a relatively low predetermined level,i.e., 4 kilovolts. The red light output increases sharply withincreasing electron energies to about 10 kilovolts, at which points theelectrons begin to pass through the particles 33 rather than to transferincreasing amounts of energy to the particles. In practice, theparticles 33 are typically not of precisely uniform size, so that thevoltage level at which complete penetration is obtained is notcompletely sharp. Thus, the curve 33A may not fall Off or even becomecompletely level, but rather, as illustrated, may rise slightly withfurther large increases in accelerating potential. This furtherincrease, however, is not considered substantial in relation to the rateof rise exhibited, for example, in the region between four and eightkilovolts. If the particles are kept to a relatively more uniform size,the response curve may level out at higher electron energies or evenfall off to lower levels.

At a relatively high predetermined level of accelerating voltage, i.e.,12 kilovolts, the electrons which pass through the gaps between theparticles 33 begin to penetrate the barrier layer 27 on the greenphosphor particles, and these particles 27 then emit green light inamounts which increase with increasing electron energies. Similarly, ata still higher energy level or threshold, i.e., 16 kilovolts, theseelectrons which do not strike a particle 33 begin to penetrate therelatively thick barrier layer 31 of the particle 23, and this particlealso begins to emit blue light in amounts which increase with increasingelectron energies. Preferably, the rate of rise of the light output ofthe blue phosphor particles 23 is greater than that of the greenphosphor particles 21, so that at some relatively high acceleratingpotential, e.g., 24 kilovolts, the blue light output substantiallyequals the green light output.

As noted previously, the particles 33 are scattered and thus there aresubstantial gaps 34 therebetween through which the green and bluephosphors may be energized independently of the electrons which strikethe red particles. Accordingly, the energy or voltage thresholdexhibited by the green or blue phosphor particles is a functionsubstantially only of their respective barrier layer.

Screen 17 comprises all three type of phosphor particles and, as may beseen from FIG. 3, these different phosphors are energized cumulativelywith increasing electron energies. Thus, screen 17 emits red light atthe relatively low accelerating voltage level; a mixture of red andgreen light at the intermediate accelerating voltage level; and amixture of red, green and blue light at the highest accelerating voltagelevel. The mixture of red and green is, in etfect, a warm achromaticlight while the mixture of red, green and blue is essentially a coolachromatic light. Thus the red record is displayed in red light, thegreen record is displayed in warm achromatic light, and the blue recordis displayed in cool achromatic light. As is explained in greater detailin copending application Ser. No. 450,705, filed Apr. 26, 1965, (nowabandoned) such a display presents a color reproduction which ispleasing in color balance and subjectively appears to include hues ofgreater saturation than are actually present in the colorimetric sense.Since the red phosphor particles do not emit light in amounts whichincrease substantially above a predetermined level, the display is notdominated by red light emitted from the red phosphor which comes onfirst and the display subjectively includes the cool COlOrs such as blueand green, even though these colors are actually displayed in relativelyunsaturated light.

While a three-color system has been disclosed, it is to be understoodthat a two-color screen may be provided by including only a singlephosphor in the underlying layer 19. This single phosphor preferablythen emits cyan light and thus, when both it and the red phosphor areenergized at relatively high electron energies, a substantially neutralcolor is obtained.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. A color display screen which produces light of different colors inresponse to impinging electrons having different energies, said screencomprising:

a first layer of particles of a first phosphor which when energized byelectrons having energies above a relatively high predetermined levelemits light of a first color; and

a discontinuous layer of particles of a second phosphor overlying saidfirst layer, said second phoshpor particles emitting light of a secondcolor when energized by electrons having energies above a relatively lowpredetermined level, each of the second phosphor particles beingrelatively small in relation to the thickness of each of said firstphosphor particles and being scattered over said first layer with gapstherebetween, said particles being of a maximum size such that onlyelectrons having energies above said relatively high predeterminedenergy level which strike said particles of said second phosphor willpass therethrough to produce substantially no more light of said secondcolor than is produced by electrons having energies just equal to saidrelatively high level, whereby electrons having energies below saidrelatively high energy level produces light only of said second colorand electrons having energies above said relatively high energy levelproduce light of a color which is a mixture of said first color whichincreases with increasing electron energies with a substantiallyconstant amount of said second color.

2. A screen as set forth in claim 1 wherein said particles are in theorder of about 0.1 to 1.0 micron in diameter.

3. A screen as set forth in claim 1 wherein said second phosphor emitsred light and said first phosphor emits light of a relatively shortwavelength.

4. A color display screen which produces light of different colors inresponse to impinging electrons having different energies, said screencomprising:

a first layer of particles of a first phosphor which when energized byelectrons having energies above a relatively high predetermined levelemits light of relatively short wavelengths; and

a discontinuous layer of particles of a second phosphor overlying saidfirst layer, said second phosphor particles emitting light of relativelylong wavelengths when energized by electrons having energies above arelatively low predetermined level, the particles of said secondphosphor being relatively small in relation to the thickness of theparticles of said first layer and being scattered over said first layerwith gaps therebetween, said particles being in the order of about 0.1to 1.0 micron in size so that only electrons having energies above saidrelatively high predetermined energy level which strike said particlesof said second phosphor will pass therethrough to produce substantiallyno more light of said relatively long wavelengths than is produced byelectrons having energies just equal to said relatively high level,whereby electrons having energies below said relatively high energylevel produce light only of said relatively long wavelengths andelectrons having ener-gies above said relatively high energy levelproduce light of a color which is a mixture of said short wavelengthlight which increases with increasing electron energies with asubstantially constant amount of said long wavelength light.

5. A color display screen which produces light of different colors inresponse to impinging electrons having different energies, said screencomprising:

(a) a first layer of first particles of a first phosphor of silveractivated zinc-cadmium sulfide, the ratio of zinc to cadmium being about:20, coated with a thin surface barrier layer comprising silica, saidfirst particles having diameters on the order of about 16 microns andemitting light of a relatively short wavelength when energized byelectrons having energies above a relatively high predetermined level,dependent upon thickness of said barrier layer; and

(b) a discontinuous layer of second particles of a second phosphoroverlying said first layer, said second phosphor particles emittinglight of relatively long wavelengths when energized by electrons havingenergies above a relatively low predetermined level, said secondparticles having diameters on the order of about 0.1 to 1.0 micron sothat electrons having energies above said relatively high energy levelwhich strike said particles pass therethrough and produce substantiallyno more light of said relatively long wavelengths than is produced byelectrons having energies just equal to or below said relatively highlevel, said second particles consisting essentially of eithereuropium-activated yttrium vanadate, europium-activated yttrium oxide oreuropium-activated gadolinium oxide,

whereby upon bombardment of said screen by electrons having energiesbelow said relatively high energy level, red light is emitted, uponbombardment by electrons having energies above said relatively highenergy level, green light is emitted in amounts which increase withincreasing electron energies, but the intensity of red light is notsubstantially increased by the additional bombardment of the electronshaving energies above said relatively high energy level; and a light ofa color which is a mixture of a limited amount of red light and anamount of said green light which increases with increasing electronenergies.

6. The color display screen of claim 5 wherein said first layer alsoincludes a blue light emitting phosphor of silveractivated zinc sulfidecoated with a relatively thicker barrier layer comprising silicondioxide whereby upon bombardment by electrons having energies above athird and relatively higher energy level, blue light is emitted for amore nearly complete color spectrum depicted on said screen, withoutsubstantially increasing the red light emitted.

References Cited UNITED STATES PATENTS 3,243,625 3/1966 Levine et a1.313-92 3,290,434 12/1966 Cooper et a1 31392 X FOREIGN PATENTS 615,8121/1949 Great Britain.

Matzen 31392 X RAYMOND F. HOSSFELD, Primary Examiner 23;? 5 g V.LAFRANCHI, Assistant Examiner Koller et a1 313-92 Donahue 313-92 10 Cl.

1785 .4 Thorington et a1. 313116 X

